This invention relates to a slide valve for accurately controlling the flow of fluid. Such valves are used in a variety of fields. The valve of the present invention as here disclosed has been designed especially for use in scientific or medical apparatus, such as blood testing apparatus, but the inventive features are applicable to fluid controlling slide valves in general wherever high accuracy, long life, and high resistance to corrosion from the fluids passing through the valve are desired. The word fluids is used here in its generic scientific sense, meaning both liquids and gases.
In the prior art, slide valves of the high precision and high quality type, such as used in scientific and medical apparatus, have customarily had cylindrical slides made of a solid cylinder or rod of metal. There is no way to keep such a slide constantly tight in the cylindrical chamber in which it slides. Leagage of fluid can and frequently does occur, both longitudinally from one port to another port, and also circumferentially around the periphery of the slide, in the tiny space between the slide and the surrounding body, which space gradually becomes bigger and bigger as wear continues. Thus a large part of the surface of the slide, and of the interior surface of the body surrounding the slide, becomes subject to contamination by and possible corrosive action from one or more of the fluids passing through the ports of the valve.
Moreover, the condition is made worse in those situations where the function to be performed by the valve requires that one port at one longitudinal location in the valve slide be connected with another port at a different longitudinal location in the valve slide, or perhaps at a different lateral location. In the conventional construction, any connecting channel for connecting two ports of the slide to each other is formed on the outer surface of the slide, and any fluid passing along this connecting channel necessarily comes into contact with the adjacent wall of the valve body, providing additional opportunity for corrosion in this area of the body, quite aside from the corrosion resulting from leakage which can not be eliminated as a cylindrical valve slide wears.